The invention relates to an apparatus and to a method for handling individual wafers that are at least temporarily in an essentially horizontal position and that have a centre and an edge, the apparatus comprising at least one supporting part with supporting areas for supporting a wafer in the edge region of the latter and at least one holding part with holding areas for gripping the edge of this wafer, with the supporting areas comprising at least three supporting points and the holding areas comprising at least two holding points, and with the at least two holding points being arranged in such a way that they can be moved relative to the supporting points andxe2x80x94to grasp the waferxe2x80x94relative to one another.
Wafers, i.e. flat, essentially circular, monocrystalline silicon discs, which are used to produce semiconductor products, are handled in clean or ultraclean rooms that satisfy special requirements and are known per se. To eliminate or at least minimize contamination or soiling of the surfaces of the wafers, automated handling is moreover preferably employed for the wafers. After or between cleaning processes, for example, the wafers are sLacked in magazines. These magazines have standardized dimensions and can be stored and transported securely in cassettes or transport boxes. The wafers often rest by their edge region on two at least approximately horizontal rails of the magazines and thus form a vertical stack of wafers. To remove discs or wafers of this kind from such magazines, in which they occupy an essentially horizontal position, or to deposit them in these magazines, either the entire stack of wafers is moved or individual, possibly predesignated, wafers are removed from the magazine or inserted into it. Preferably, it should be possible, after removing a wafer from a magazine, to deposit it at any desired location.
The prior art includes apparatus for transporting individual wafers that has simple gripping apparatus. Such apparatus is only suitable for transporting essentially vertically aligned, upright wafers. The prior art includes further apparatus and robots that hold a wafer by means of a vacuum: e.g. U.S. Pat. No. 4,886,412 has disclosed a robot for handling essentially vertically aligned wafers, while WO 98/02906 has disclosed a robot for handling essentially horizontally aligned wafers. Each of these robots is thus essentially tied to one wafer alignment, and this can be a disadvantage because the applications of these robots are limited.
EP 0 365 589 has disclosed an apparatus of the generic type and a method of the generic type for handling individual silicon discs or wafers stored essentially horizontally in magazines: a device for transporting an individual silicon disc having moving wheel-shaped carriers that can be moved relative to one another between a closed positionxe2x80x94in which a wafer can be carried exclusively through the contact between the circumference of the wafer and the carriersxe2x80x94and an open positionxe2x80x94in which a wafer can be arranged between the carriers. To pick up a wafer, a respective support having at least two wheel-shaped carriers is moved from each of two opposite sides partially into a magazine filled with wafers until the edge region of the selected wafer touches the wheel-shaped carriers on their oblique supporting areas and on their cylindrically shaped holding areas (cf. FIG. 4). The wafer picked up and fixed in this way is transported out of the magazine by joint unilateral movement of the two supports. This apparatus and this method have the disadvantage that if a wafer has been moved out of the magazine one of the two supports extends through the magazine (being made longer for this purpose), with the result that it is not possible to move the wafer in a different direction to that for removal of the latter from the magazine without transferring the wafer to a further transfer robot, such as that disclosed in U.S. Pat. No. 4,923,054, the gripping mechanism (cf. FIG. 6) of which corresponds essentially to that in EP 0 365 589. However, because of its overall height the gripper described in U.S. Pat. No. 4,923,054 is not suitable for direct removal of a wafer lying between two immediately adjacent wafers from a filled magazine because it cannot be inserted between two wafers of a filled magazine.
Another disadvantage of the apparatus and the method described in EP 0 365 589 could be regarded as the fact that it is only possible to remove wafers from magazines or place them in the latter if these magazines have been removed beforehand from the cassette that protects them. If use is made of cassettes in which a transfer opening or door is opened on one side for the removal of a wafer, it is not possible to use this apparatus.
U.S. Pat. No. 4,923,054 has disclosed another apparatus for handling a wafer, which comprises a two-armed robot, the front arm of which comprises a support plate for supporting a wafer. However, this robot cannot perform vertical movement, and the magazine must therefore be lowered somewhat to enable the robot arm with the wafer resting on it to be removed smoothly from the support rails of the magazine. This distribution of the movements between two different devices requires a coordinating control system. Moreover, the wafer is touched approximately at its centre; although this naturally takes place on the rear side of the wafer, this is associated with a certain risk of contamination.
EP 0 858 866 discloses another apparatus of the generic type. This relates to a mechanical robot arm for transferring a wafer. A unilateral force is exerted on the wafer 35 by means of holding fingers 102, 104, pressing the wafer against a holding bridge 106 (cf. FIG. 3 and FIG. 5 with the holding fingers in the closed state and FIG. 7, where they are in the open state). EP 0 858 866 thus also discloses that the wafer performs a movement subject to friction. With the solution proposed there, it may be possible to reduce this friction, but it cannot be avoided.
U.S. Pat. No. 5,380,137 has disclosed another apparatus for heat-treating wafers. This apparatus comprises an arm for transferring a wafer between a wafer magazine (xe2x80x9cboat 10xe2x80x9d, cf. FIG. 1), in which a multiplicity of wafer support plates (xe2x80x9csupport plates 11xe2x80x9d, cf. FIG. 2) are stacked vertically with regular gaps in between, and a cassette (xe2x80x9ccassette 50xe2x80x9d, cf. FIG. 4), in which the wafers are likewise to be stacked vertically with regular gaps in between. A wafer-lifting mechanism (xe2x80x9cpush up mechanism 20, 21xe2x80x9d) and a carrying fork (xe2x80x9cfork 31xe2x80x9d) co-operate. The carrying fork 31 has a recess 65 to ensure that, as it enters a stack, it does not collide with the carrying pin 22, which is situated on the axis of insertion and is connected to the lifting mechanism 21 (cf. FIG. 15). With this apparatus, wafers can only be transported in a horizontal position and stacked vertically.
Another apparatus of the generic type for handling individual flat glass substrates during the production of LCD displays and wafers is known from U.S. Pat. No. 5,374,147. The apparatus for transferring an LCD substrate in a vacuum comprises a first table, on which the LCD substrate is secured in such a way that its surface is aligned essentially horizontally. The substrate is placed on the table or on silicone rubber support elements that are preferably provided and is positioned by means of holding elements (which are immovable or can clamp the substrate between them). The apparatus disclosed allows substrates to be held and transported exclusively in a horizontal position.
The object of the present invention is to provide an apparatus and a method for handling wafers that make it possible to pick up individual essentially horizontal wafers, in particular wafers lying in a magazine, essentially without friction and to transport and deposit them in virtually any desired position.
According to a first aspect of the invention, this object is achieved by an apparatus for handling individual wafers that are at least temporarily in an essentially horizontal position and that have a centre and an edge, with the apparatus comprising: at least one supporting part with supporting areas for supporting a wafer in the edge region of the latter and at least one holding part with holding areas for gripping the edge of this wafer, with the supporting areas comprising at least three supporting points and the holding areas comprising at least two holding points, and with the at least two holding points being arranged such that they can be moved relative to the supporting points and, to grasp the wafer, relative to one another. At least one of these holding points is arranged on a rotatable rod designed, for reliable holding of the wafer, as a holding part, with this rotatable rod extending coaxially with an axis running through the centre of the wafer and essentially parallel to the surface of the wafer. Advantageous modifications and developments of the apparatus according to the invention are discussed.
According to a second aspect of the invention, this object is achieved by a method for handling individual wafers that are at least temporarily in an essentially horizontal position and that have a centre and an edge, using an apparatus that comprises at least one supporting part with supporting areas for supporting a wafer in the edge region of the latter and at least one holding part with holding areas for gripping the edge of this wafer, with the supporting areas comprising at least three supporting points and the holding areas comprising at least two holding points, and the at least two holding points being arranged such that they can be moved relative to the supporting points and, to grasp the wafer, relative to one another. According to the method, the wafer is raised by raising the supporting areas and held by moving the holding areas relative to the supporting areas and moving at least two holding points relative to one another; at least one of these holding points is arranged on a rotatable rod designed as a holding part that extends coaxially with an axis running through the centre of the wafer and essentially parallel to the surface of the wafer. Advantageous modifications and developments of the method according to the invention likewise are disclosed.
Preferred embodiments of the invention are illustrated more or less schematically as examples in the figures, but these examples are not in any way intended to restrict the scope of the present invention.